1. Field of the Invention
The present invention relates to allocating current from a distributor. More particularly, the present invention relates to allocating current from a distributor having a maximum rated current capacity, among a plurality of load circuits, including a variable load circuit that benefits from a full load current allocation but is operable at a lower current allocation, for example a charging circuit for an electric vehicle battery.
2. Description of the Related Art
Electrical distributors, for example distribution panels, are conventionally designed such that the aggregate current carrying capacity of all branch circuits is significantly higher than that of the main circuit breaker. In other words, the design assumes that not all branch circuits will supply loads—let alone full loads—simultaneously. Each branch breaker is limited to relatively small load capacities, a standard which is derived from statistical analysis of standard consumption patterns. Also worth noting is that the main panel breaker circuit is often characterized by periods of electrical current demand well below its maximum capacity.
When demand for current exceeds the capacity of the distributor, load-shedding is a commonly used method to ensure that the combined loads do not exceed the maximum rated current capacity, typically as established by the main breaker, but more generally established by the lowest capacity component in the main circuit. Through shedding, branch loads are selectively disconnected or disabled when this capacity is approached. This method is used on common branch circuits with fixed or strictly limited variable loads. When the aggregate load of all branch circuits reaches the current capacity rating of the main breaker in the distribution panel, selected loads are switched completely off to reduce the total load on the system. There are no intermediary stages of such load-shedding; either a branch is on or it is off.
This arrangement is sufficient where the contemplated current load on each branch circuit is either fixed or varies within relatively narrow prescribed limits. However, when the current load in a branch circuit is highly variable, and might even rise above the capacity of the main breaker itself, a more flexible, robust and effective solution is necessary and provides the motivation for this invention.
A case in point is opportunity charging for batteries. Batteries can be charged at various rates. When spare capacity exists, there is an opportunity to charge batteries faster. When capacity is limited, charging can be reduced or postponed by shedding a variable amount of the load.
It is common for battery chargers to employ current-control circuitry, but this circuitry is limited to battery-state sensing in order to maximize battery life and prevent damage, not to the sensing of available supply current. By enabling the charger to maximize the charge rate of sensitive batteries, the danger of the battery undergoing excessive deep-discharge cycles is minimized and battery life thereby extended.
As battery-powered electric vehicles become more common, better opportunity charging arrangements will be needed to enable smaller household circuits, with their limited current capacity, to efficiently and effectively recharge vehicle batteries. Such arrangements would make larger charging currents available on demand—when capacity is available—in order to reduce the time it takes to charge a battery bank. As other demands are placed on the distributor, the battery charging load can be partially or completely shed.
Such opportunity charging arrangements would allow the use of a charger branch circuit with much higher current ratings than would normally be available. There are many examples of current sensor technology applied to the measurement, display and shedding of current loads in both household and industrial settings, but none appear to apply the signals thus derived to the variable control of specific current loads in those environments.